Sealing elements consisting of a loop of flexible steel are already known (German Offenlegungsschrift No. 16 00 964 and U.S. Pat. No. 3,460,457) for sealing polygonal gate-type shut-off valves for large pipes which are used for conveying hot dust-laden gases. These sealing elements are gripped at both ends of the loop-shaped cross-section and engage with the main part of the loop body between the two parts to be sealed, between which the loop-shaped sealing element is pressed flat.
These known constructions have various disadvantages. Because of the loop-shaped construction and the engagement of the sealing element between the two elements which are to be sealed against each other (against which the sealing element rests at two points in all), the individual sealing elements require a large amount of material and a considerable amount of space for their installation.
The prior art also includes a shut-off device (German Offenlegungsschrift No. 25 02 240) in which the sealing element is formed by a strip of spring steel with a U-shaped cross-section gripped at the free ends of the two arms of the U on one of the two elements which are to be sealed against each other (gate valve housing or gate) and in its central region between the two gripping positions is in sealing contact with the other of the two elements. The gripped ends of the spring steel strip are in this case parallel to one another.
On loading of such a sealing element it is possible--because of the limited deformability in the direction of the gripped ends--for bending at a sharp angle to occur. In addition, since the type of deformation cannot be determined in advance no specific contact pressures can be achieved. Finally, deformation of the known sealing element can lead to sharply increasing contact pressures and thus to uncontrollable wear.
The object of the invention, therefore, is to avoid the defects of the known constructions and to provide a shut-off device which ensures even in dust-conveying pipes under high thermal load satisfactory functioning and a long operational life of the sealing elements.